Method for making rayon filaments



Nov. 5, 1963 w. c. RICHARDSON 3,109,699

METHOD FDR MAKING RAYON FILAMENTS Filed April 30. 1962 m yenfor [MN/0m 6. Ham/U500 By Ms af/omeys ALWWM/Q4W- United States Patent 3,109,699 METHOD FOR MAKENG RAYON FILAMENTS William C. Richardson, Mobile, Ala., assignor to Courtanlds North America Inc., New York, N.Y., a corporation of Alabama Filed Apr. 30, 1962, Ser. No. 191,004. 4 Claims. (Ci. 18-54) This application relates to the manufacture of high tenacity rayon filaments and in particular to the manufacture of high tenacity rayon staple fiber.

In recent years there has appeared on the market a new type of rayon fiber characterized by a high degree of crystallinity, a high tenacity, a more or less circular, non-crenulated, cross section and the absence of any appreciable skin-core structure. In general such fibers are made by extruding a substantially unripened viscose, the cellulose of which has a high degree of polymerization, into an aqueous bath relatively low in regenerative power, and stretching the filaments to achieve orientation while they remain substantially unregenerated.

Various specific techniques have been suggested for carrying out this general process. In particular it has been suggested that formaldehyde be incorporated in the spinning bath to retard regeneration of the filaments and that the filaments be stretched in a subsequent hot bath containing, say, 14% acid. This process, when operated under optimum conditions, and particularly when used for the manufacture of continuous filaments can give excellent results. However, it is open to several drawbacks.

Thus, for example, in the manufacture of staple fiber it is necessary that the filaments be substantially entirely regenerated before they are cut.

Cutting necessarily involves relaxation and if the filaments, having been stretched, are allowed to relax before they are regenerated, the effect of the stretch is largely lost. The hot acid stretch bath used in prior processes, while it is regenerative for filaments spun in high zinc baths, is not very regenerative for filaments spun in the presence of formaldehyde. The cellulose xanthate methylol hydrate formed as the result of such spinning must be hydrolyzed in regeneration and its hydrolysis is suppressed by the presence of PH ions.

Because acid stretch baths are inefiicient for regeneration it is necessary either to greatly extend the travel of the filaments through the bath or to add a subsequent separate regeneration step. Neither of these alternatives is very attractive, particularly when staple fiber is being made, since it is ordinarily desirable to cut the staple as soon as possible and conduct the washing, desulfurization, and like after treatments on the cut fiber.

In addition, the hot dilute acid bath, which always contains some formaldehyde carried over by the filaments, favors the formation of various undesirable by-products, notably trithiane, which tend to discolor the threads and are diflicult to remove.

In accordance with the invention these and other problems are overcome by conducting the stretching operation in the presence of steam. By avoiding the use of a liquid bath of dilute acid, regeneration of the filaments is accelerated, permitting the filaments to be relaxed as soon as they are removed from the stretching step. Moreover, formation of trithiane is suppressed.

The invention, therefore, envisions, in a method for making high tenacity rayon filaments wherein viscose is extruded into an aqueous acid coagulating bath in the presence of small quantities of formaldehyde to form filaments, the filaments are removed from the coagulating bath while not more than about 20% regenerated, and are then stretched, the improvement which comprises stretching said filaments while they are in contact with steam.

THE VISCOSE The viscose used in the present process is preferably made from pulp whose cellulose has a high degree of polymerization, (DP), say over 600. Of course, cellulose having lower DP, say 300-600, can be used, at a sacrifice of tenacity in the product. The viscose can be manufactured in conventional manner, but preferably the alkali cellulose is not aged, and the viscose is preferably spun without substantial ageing. It may contain, for example, from 2 to 7% cellulose, and from 2 to 9% NaOH. It may have a salt (NaCl) figure of 12 to 23, a gamma number of not less than 60, normally 73 to 90 or higher, and a viscosity (ball fall) of 30 to 400 seconds, determined by the cellulose content and DP of the viscose.

SPINNING BATH omitted or, if present, is maintained below about 0.2%.

The bath will also contain a small quantity normally between about 0.5 and about 2.0%, preferably between about 0.5 and about 1.0%, of formaldehyde, to retard regeneration. If desired, the formaldehyde may be added to the viscose. However, if this is done it is recommended that the techniques described in the copending application of Klein et al., Serial No. 192,322, filed May 4, 1962, in common ownership herewith, be employed, i.e. that the formaldehyde be in substantially monomeric form prior to injection and that it be injected just prior to spinning.

The temperature of the spin bath will normally range from say 20 C. to 35 C.

The spinning speed will normally be determined by the viscosity of the viscose. It can range from say 20 m./m. to 50 m./rn. The extrusion ratio is preferably around 0.5, say from about 0.2 to 0.7. The residence time of the filaments in the bath will be determined by the spinning speed, extrusion ratio and stretch to be applied. In most instances it will be between about 1 and about 4 seconds.

STRETCH CONDITIONS As noted above, the viscose is preferably spun at a gamma value of about 75 to about 90. As the coagulated filaments are removed from the bath, the gamma value is still above about 65, or not less than of its value prior to spinning. Thus the filaments are not more than say 20% regenerated, are plastic and are capable of being stretched to a large degree. In accordance with the invention, the filaments are now passed through an atmosphere of steam and in said atmosphere are stretched by between about 150 and about 350% to achieve orientation.

The steam is preferably saturated steam and is at a temperature of say to C. The use of saturated steam maintains the filaments sufficiently plastic so that a high degree of orientation is obtained.

PRACTICING THE INVENTION The drawing is a schematic diagram illustrating the practice of the invention.

Referring to the drawing, viscose is pumped by conventional means (not shown) through a tube 10 and spinnerette 11 into a weakly acid spinning bath 12, containing formaldehyde. As shown in the drawing, spinning is preferably carried out in a vertical direction, since a rather short bath travel of say 3 to 12 inches is generally preferred, The filaments 13 are carried over a roller 14 and then through a steam treating device 15 to a roller 16 which is driven at a higher speed than roller 14, thus stretching the filaments in the device 15.

The device 15 may be of any suitable construction which is adapted to provide and maintain a steam atmosphere around the filaments 13. As shown in the drawing it may comprise an inner tube 17 having perforations 18 in its walls, enclosed in an outer shell or manifold 19. An inlet pipe 20 is provided for furnishing steam to the manifold and a reservoir 21 and drain pipe 22 may be furnished for removing condensate.

In operation steam is furnished through line 20. It passes through the perforations 18 into the tube 17 and maintains a hot, moist atmosphere in the tube under which conditions the filaments are stretched. Condensate drains into wall 21 and is removed through pipe 22.

The filaments 13, as they are taken off roller 16, are at least 90% regenerated. They are preferably immediately cut by a conventional staple cutter 23 to form staple fiber 24. This is allowed to fall onto a continuously moving belt 25 where it forms a blanket 26. In that form the fiber can be subjected to the usual washing treatments conventional in the art.

The invention will be further described with reference to the following specific example which is cited merely as illustrative of the process and is not to be taken as in any way limiting the invention beyond the scope of the appended claims.

Example A viscose containing 5.00% cellulose and 6.44% NaOI-I was spun at a salt figure of 18 :75) and a ballfall viscosity of 141 seconds into a spinning bath containing 7.1% H 50 12% Na SO 0.5% HCHO and no zinc salts, at 29 C. The extrusion ratio was about 0.4. After a bath travel of 11 inches the filaments were stretched in saturated steam at substantially atmospheric pressure by 192%, and then immediately cut up into staple. As they emerged from the spinning bath the filaments were about 20% regenerated, having a gamma value of about 50. Upon emerging from the steam tube (similar to that shown in the drawing), the filaments were about 90% regenerated. Regeneration was completed by the sluice acid (1% H used to wash the cut filaments out of the cutter.

The product had a filament denier of 1.59, a dry tenacity of 4.88 g./den., a wet tenacity of 4.08 g./den., a dry elongation of 6.2% and a wet elongation of 7.8%.

.What is claimed is: V

1. A method for making high tenacity rayon filaments which comprises extruding viscose in the presence of formaldehyde into an acid coagulating bath low in regenerative power and containing not more than 0.2% of a zinc salt, to form filaments, removing the filaments from said bath while they are not more than 20% regenerated, stretching said filaments in an atmosphere of saturated steam having a temperature between about 90 and about 110 C. to orient said filaments, and maintaining said filaments in said steam atmosphere until they are at least 90% regenerated.

2. The method claimed in claim 1 wherein the steam is saturated steam at a temperature of between about 90 and about 110 C. V

3. A method for making high tenacity rayon staple fiber which comprises extruding substantially unripened viscose in the presence of formaldehyde into an acid coagulating bath containing not more than about 9% H not more than about 18% Na SO and not more than 0.2% ZnSO removing the filaments from the bath while they are not more than about 20% regenerated, passing the filaments through saturated steam having a temperature between about and about C. and simultaneously stretching the filaments, maintaining said filaments in contact with said steam until they are at least 90% regenerated and then cutting said filaments to form staple fiber.

4. The method claimed in claim 3 wherein the filaments are stretched between about and about 350%.

References Cited in the file of thispatent UNITED STATES PATENTS 

1. A METHOD FOR MAKING HIGH TENACITY RAYON FILAMENTS WHICH COMPRISES EXTRUDING VISCOSE IN THE PRESENCE OF FORMALDEHYDE INTO AN ACID COAGULATING BATH LOW IN REGENERATIVE POWER AND CONTAINING MIXTURE NOT MORE THAN 0.2% OF A ZINC SALT, TO FORM FILAMENTS, REMOVING THE FILAMENTS FROM SAID BATH WHILE THEY ARE NOT MORE THAN 20% REGENERATED, STRETCHING SAID FILAMENTS IN AN ATOMSPHERE OF SATURATED STEAM HAVING A TEMPERATURE BETWEEN ABOUT 90 AND ABOUT 110*C. TO ORIENT SAID FILAMENTS, AND MAINTAINING SAID FILAMENTS IN SAID STEAM ATMOSPHERE UNTIL THEY ARE AT LEAST 90% REGENERATED. 